Antenna



Patented Nov. 18, 1947 ANTENNA Harvey Kees-and Fay Gehres, Evansville, Ind., assignors to Electronics Research, Inc., Evansville, Ind., a corporation of Indiana Application February 20, 1946, Serial No. 648,966

Claims. 1

This invention relates to improvements in antennae for the reception and transmission of high frequency signal energy, and is particularly concerned with antenna systems for use in aircraft or like vehicles. It is an object of the invention to provide an antenna offering minimum drag or wind resistance and having substantially improved efiiciency as compared with more conventional antennae of comparable dimensions.

Although the advantages inherent in the mounting of an antenna Within the envelope or skin of aircraft are at once apparent, the practice in this field has been largely confined to externally disposed antenna structures, owing principally to the difiiculties encountered in designing an inexpensive antenna system which is sufiiciently compact to be fitted within the limited space available in the aircraft fuselage. It is therefore a further object of the invention to provide an antenna system which may be housed entirely within the fuselage so as to provide a min imum of interruption or retardation of air flow over the external surface of the aircraft,and elimination of variation in operating characteristics resulting from changing weather conditions,

the antenna being characterized by small size and high efliciency, having a field pattern of generally uniform intensity in planes normal to the surface into which it is faired.

A further object of the invention is to provide an antenna system including an antenna and a housing therefor constituting. a unitary assembly, capable of being mounted readily as a unit in a suitable opening in the vehicle skin.

Further objects and features of the present invention will be apparent. from the following description taken in connection with the accompanying drawings, in which Figure 1 is a view in perspective of an antenna unit constructed in accordance with the principles of the inventio showing the unit faired into a substantially plane surface;

Figure 2 is a longitudinal sectional view of the unit shown in Figure 1;

Figures 3 and 4 are diagrammatic representations of alternative circuits suitable for use in the practice of the invention.

In order to facilitate an understanding of the principles of the invention, reference is made herein to the embodiment illustrated in the drawing, and specific language is used to describe the same. It will nevertheless be understood that no limitation of the'scope of the invention is thereby intended, various furthermo'difications and alterations of the illustrated structure, falling within the broad principles of the invention, being contemplated herein.

As shown in the drawings, the invention in its preferred form consists essentially in an antenna element ID, a housing I l, and a variable-condenser l2, the antenna being grounded at one end, con nected to ground at its opposite end through the Variable condenser, and being connected to a transmission line I5, for instance the conventional coaxial cable, at a point adjacent to but spaced from its'grounded end, the last named point being so selected as to match the impedance of the transmission line. Alternatively, series condensers may be employed at the high voltage end of the antenna, the signal energy being fed to the antenna intermediate the condensers.

The housing H may be formed principally of metal to provide a generally rectangular panshaped chamber having its outer, electrically open side covered with a closure sheet ll of suitable noneconducting material, for example plastic material, plexiglass, or the like, the latter being suitably sealed in position to exclude moisture from-the interior of the housing. The housing is formed with a peripheral flange l8, and is received within an aperture in the surface 25 or vehicle skin, the flange l8 overlying the skin and being secured thereto in any convenient manner, for instance by riveting. The precise shape of the housing is not a critical factor. Since the housing is grounded to the vehicle skin, the grounded end of the antenna l0 may be bonded directly to the adjacent end wall of the housing, for instance by brazing or welding, thus forming a convenient method of supporting and electrically connecting the antenna. At its other end the antenna is provided with a depending flange or leg 22 which may be bonded to the frame or stator of the condenser 12, the latter being secured by insulating means on the adjacent end wall of the housing I I, so that the antenna is thus similarly conveniently mounted and electrically connected through the condenser to ground at the high voltage end. It, will be noted that the condenser is further removed from the electrically open face of the housing ll than is the antenna itself. This is important in insuring stability of operation, since that portion of the system which develops the highest voltage is further from the vehicle surface, with the result that the change in frequency of the antenna when the covering plate I! is wet is minimized.

A conventional coupling 23 for engagement with the outer conductor of a coaxial line I5 is mounted in the end wall of the housing ll adjacent the grounded end of the antenna, the inner conductor 24 of the coaxial line being electrically connected to the antenna at a point 25 which is spaced from the point of bonding of the antenna to the housing. A convenient method of determining the proper location of this point is to adjust the connection lengthwise of the antenna until the best standing wave ratio is established on the transmission line when the line is fed by a signal of the frequency to which the antenna is adjusted by the condenser [2.

The antenna is formed of metal and may assume various shapes. We have found by a test, however, that the form of antenna illustrated in the drawing is most efiicient, namely an elongated flat strip having a width several times its thickness. Satisfactory results have been achieved, for instance, by the use of a strip of one-quarter inch thickness, 4 inches wide, and 8 inches long, the internal length of the housing for such an antenna being about 10 inches long. It will be appreciated that such a construction is extremely compact and lends itself well to mounting in vehicles such as airplanes in which available space is at a minimum.

When compared with an externally mounted dipole of the same length, the antenna just described developed substantially the same voltage in the reception of '75 megacycle signals, both antennae being connected to a field strength meter having a 50 ohm non-reactive input. The f aired antenna gives a field pattern which is fairly uniform over a wide angle when measured either in a plane containing the line of flight or in a plane normal thereto, and is particularly effective in the reception of marker beacon signals, for which purpose the antenna unit is faired into the under-surface of the plane fuselage. The drag offered by the unit is, of course, negligible.

For convenience in defining the invention, the antenna housing, when disposed entirely within the vehicle skin so that the electrically open side thereof is substantially flush with the skin, is described as faired into the vehicle skin. The outer face of the housing may be left open, but i preferably closed by a non-conducting sheet to exclude moisture from the interior of the housing and the several elements of the system contained therein. It will be appreciated that from the standpoint of electrical performance, the nonconducting closure sheet effects no function.

The electrical system in which the antenna is employed makes possible the substantial reduction in length of the antenna without decrease in efficiency, but careful adjustment of the effective length of the antenna by initial setting of the top-loading condenser I2 is important in order that optimum results may be achieved. To facilitate this adjustment, the control shaft by means of which the condenser rotor is operated may be brought through the end wall of the housing on which the condenser is mounted. The connection between the live conductor of the transmission line and the antenna, having once been so determined as to match the impedance of a given transmission line, need not be altered. It is therefore possible to assemble the entire antenna structure as a unit in the fuselage merely by cutting a suitably dimensioned opening in the skin and riveting or welding the peripheral flange IS in position.

As illustrated more particularly in the modified circuit shown in Figure 4 of the drawing, the antenna element IE1 may be fed at the high voltage end, rather than adjacent the grounded end as shown in Figure 3. Thus we may connect the high voltage end of the antenna through series condensers l2 and 32, the latter being a fixed condenser having such capacity as to match the impedance of the transmission line when the latter is connected between the two condensers. Other elements employed in this modified construction may be similar to those hereinbefore described and may be similarly arranged, the antenna being grounded at its opposite end by bonding to the housing wall. As in the form of the invention illustrated in Figure 3, the antenna is tuned to the desired signal frequency by adjusting the variable or top-loading condenser I2,

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In an antenna system for aircraft and like vehicles, the combination with a conducting antenna housing faired into and electrically connected with the vehicle skin and having a nonconducting side substantially flush with the skin, of an elongated antenna supported in said housing, having one end thereof directly grounded and the other end thereof capacitively coupled to ground, and a signal transmission line connected to said antenna at a point adjacent to the grounded end but spaced therefrom to the extent required to match the impedance of the transmission line.

2. In an antenna system for aircraft and like vehicles, the combination with a conducting antenna housing faired into and electrically connected with the vehicle skin and having a nonconducting side substantially flush with the skin, of an elongated antenna supported in said housing, having one end thereof directly grounded and the other end thereof capacitively coupled to ground, and a signal transmission line connected to said antenna at such a point that the impedance of the transmission line is matched.

3. In an antenna system for aircraft and like vehicles, the combination with a conducting antenna housing faired into and electrically connected with the vehicle skin and having a nonconducting side substantially flush with the skin, of an elongated antenna supported in said housing, having one end thereof directly grounded and the other end thereof capacitively coupled to ground, said capactive coupling being spaced further than said antenna from the non-conducting side of said housing.

4. In an antenna system for aircraft and like vehicles, the combination with a conducting antenna housing faired into and electrically connected with the vehicle skin and having a nonconducting side substantially flush with the skin, of an elongated antenna supported in said housing, having one end thereof directly grounded and the other end thereof capacitively coupled to ground through series condensers, and a signal transmission line connected intermediate said condensers.

5. In an antenna system for aircraft and like vehicles, the combination with a, conducting antenna housing faired into and electrically connected With the vehicle skin and having a nonconducting side substantially flush with the skin, of an antenna supported in said housing, having one end thereof directly grounded and the other end thereof capacitively coupled to ground, said antenna comprising a fiat metal strip having a width at least several times its thickness.

6. In an antenna system for aircraft and like vehicles, the combination with a conducting antenna housing faired into and electrically connected with the vehicle skin and having a nonconducting side substantially flush with the skin, of an antenna supported in said housing, having one end thereof directly grounded and the other end thereof capacitively coupled to ground, said antenna comprising a flat metal strip bonded at one end to said housing and mounted at its opposite end on said capacitive coupling.

7. An antenna unit for high frequency signal energy, said unit comprising a conducting housing having an electrically open side, an antenna in said housing supported in parallelism with said open side, said antenna being electrically connected at one end to said housing, and a capacitive coupling between the opposite end of said antenna and said housing.

8. An antenna unit for high frequency signal energy, said unit comprising a conducting housing having an electrically open side, an antenna in said housing supported in parallelism with said open side, said antenna being electrically connected at one end to said housing, a capacitive coupling between the opposite end of said antenna and said housing, said coupling being disposed further from the open side of said housing than said antenna, said antenna being deflected at the said opposite end toward said coupling for connection therewith, whereby that portion of the antenna system in which the highest voltages are developed is more remote from the said open side of said housing.

9. In an antenna system for aircraft and like vehicles, the combination with a conducting antenna housing faired into and electrically connected with the vehicle skin and having a nonconducting side substantially flush with the skin, of an antenna comprising an elongated, fiat conducting strip supported in said housing, electrical connections between said housing and said antenna at opposite ends of the latter, and a signal transmission line connected to said antenna at such a point that the impedance of the transmission line is matched.

10. In an antenna system for aircraft and like vehicles, the combination with a conducting antenna housing faired into and electrically connected with the vehicle skin and having a nonconducting side substantially flush with the skin, of an antenna comprising an elongated, fiat conducting strip supported in said housing, electrical connections between said housing and said antenna at opposite ends of the latter, one of said connections comprising an impedance coupling, and a signal transmission line connected to said antenna at such a point that the. impedance of the transmission line is matched.

HARVEY KEES. FAY GEHRES.

REFERENCES CITED The following references are of record in the file of this patent:

2,418,084 Montgomery, B. E. Mar. 25, 1947 

